Windows Phone 8.1 'Blue'

Windows Phone 8.1, codenamed ‘Blue’, is the latest update to the Microsoft Windows Phone operating system. It was announced at Microsoft’s Build 2014 conference in April, with new devices like the Lumia 930 arriving later that month.

A Preview for Developers program was also announced at Build, with availability for the general public arriving on April 14th, 2014. It has been estimated that over 1.5 million devices have the 8.1 Preview installed after the first week.

All current Windows Phone 8 devices, including the Lumia 520, qualify to receive the update, which is expected to commence on July 15, though it will vary from carrier to carrier and could span 8 weeks or more.

Nokia devices are also receiving new firmware specific for Lumia phones called 'Lumia Cyan'. This firmware comes packaged with the official Windows Phone 8.1 over-the-air update.

History and Future

Following the re-launch of Windows Phone 8 back in late 2012, the 8.1 update follows on Microsoft’s planned 18-month upgrade path for their mobile operating system. While Windows Phone 8 had three feature-adding updates during its life-cycle (‘Portico’, Update 2, Update 3), the 8.1 update is a significant overhaul of the OS.

After Windows Phone 8.1 was announced (May 2014), it is expected to receive numerous General Distribution Release (GDR) updates, finally being supplanted by a spring 2015 release of ‘Threshold’ aka Windows Phone 8.2 or Windows Phone 9. The first update for Windows Phone 8.1 should wrap development in July, with a release later that summer.

Credit to : http://www.wpcentral.com/windows-phone-81